Yang Xu
Purdue University Department of Physics and Astronomy, USA
Title: Tunable two-species Dirac fermions and quantum Hall effect in dual-gated three-dimensional topological insulators
Biography
Biography: Yang Xu
Abstract
Topological insulators (TI) are a novel class of quantum matter with a gapped insulating bulk yet gapless spin helical Dirac fermions. Recently [1], we have shown surface-dominated conductance in an intrinsic 3D TI, BiSbTeSe2 (BSTS), even close to room temperature for thin samples. In high magnetic field and low temperature, thin-flake samples exhibits well-developed quantum Hall effect (QHE), where the two parallel surfaces each contribute a half-integer e2/h quantized Hall resistance, accompanied by vanishing longitudinal resistance. Such “half-integer†QHE is a hallmark of massless Dirac fermions. Further [2], we performed local and non-local electrical and magnetotransport measurements in dual-gated BSTS thin film TI devices, with conduction dominated by the spatially separated top and bottom surfaces, each hosting a single species of Dirac fermions with independent gate control over the carrier type and density. We observe many intriguing quantum transport phenomena in such a fully-tunable two-species topological Dirac gas, including a zero-magnetic-field minimum conductivity of ~4e2/h at the double Dirac point, a series of ambipolar two-component “half-integer†Dirac quantum Hall states and an electron-hole total filling factor ν=0 state (with a zero-Hall plateau), exhibiting dissipationless (chiral) and dissipative (non-chiral) edge conduction respectively. Such a system paves the way to explore rich physics ranging from topological magnetoelectric effects to exciton condensation.